It has been known for some time that vegetative death or "senescence" occurs in all races of Podospora anserina and that the rate and onset of senscence varies among different races and mutant strains. It is also known that senescence is cytoplasmically inherited in intra and interracial crosses and that mitochondrial function is involved. We have found that mitochondrial DNA from Podospora consists of a 30 micro covalently closed circle. During senescence, at a time when mitochondrial function is impaired, we made two observations: 1) a significant fraction of the mitochondrial DNA consists of a multimeric series of circles ranging in contour length from 0.9 micro to 15 micro; no circles of full length were found in senescent mt DNA, and 2) a new GC-rich fraction of mt DNA appeared. We now have two major objectives in this research proposal: A) to characterize the mt DNA with respect to replication scheme, partial denaturation mapping, restriction enzyme maps and the interracial homology of restriction enzyme fragments, and B) to investigate in detail the molecular basis for senescence. This will include the time-course of events with regard to morphological changes, low temperature spectra, function and appearance of the low molecular weight multimeric circular mt DNA. In addition, we will isolate these multimeric circles and charactrize them with respect to restriction enzyme mapping to determine whether they represent amplified DNA from a specific region of the mitochondrial genome. Mitochondrial DNA is thought to be involved in aging in Paramecium, the blow-fly and in male sterility in maize, and it is our hope that a systematic study of mitochondrial DNA during senescence in Podospora will lead to a detailed and comprehensive understanding of this important biological process.